At present, in the solder resists of consumer and industrial printed wiring boards, from the standpoint of attaining high precision and high density, liquid developing-type photosolder resists that are, upon being irradiated with ultraviolet light, developed to form an image and then subjected to final curing (main curing) by heating and/or irradiation with a light are used. Further, in response to hight densification of printed wiring boards in association with miniaturization of electronic devices, there is a demand for a solder resist having an improved workability and high performance.
Among such liquid developing-type solder resists, in consideration of environmental problems, it is the prevailing trend to use an alkali developing-type solder resist which utilizes a dilute aqueous alkaline solution as its developing solution, and such an alkali developing-type solder resist is being used in a large amount in the actual production of printed wiring board. As such an alkali developing-type photosolder resist, an epoxy acrylate-modified resin derived by modification of an epoxy resin has been commonly used.
For example, Patent Document 1 discloses a solder resist composition which comprises: a photosensitive resin obtained by adding an acid anhydride to a reaction product of a novolac-type epoxy compound and an unsaturated monobasic acid; a photopolymerization initiator; a diluent; and an epoxy compound. Patent Document 2 discloses a solder resist composition comprising: a photosensitive resin obtained by adding (meth)acrylic acid to an epoxy resin, which is produced by allowing a reaction product of salicyl aldehyde and monohydric phenol to react with epichlorohydrin, and further allowing the resultant to react with a polybasic carboxylic acid or an anhydride thereof; a photopolymerization inhibitor; an organic solvent; and the like.